1. Field of the Invention
The present invention relates to a beam-index color display unit.
2. Description of Background Information
Beam-index type color display units are constructed that a two-dimensional screen consisting of three-color phosphor stripes of R (red), G (green), and B (blue), which are arranged with regularity in the horizontal direction, is scanned by a single beam. For this reason, it is necessary to apply a feedback system to detect the horizontal scanning position of the beam, so that the phosphor stripes are correctly excited.
An example of conventional beam-index color display units is shown in FIG. 1. As shown, a two-dimensional screen 33 is formed by horizontal stripes 31 of R, G, B arranged with regularity in the horizontal direction and black stripes 32 consisting of a black opaque material which is inserted between each horizontal stripe 31. Moreover, a metal back 34 of aluminum is formed on the whole area of the screen 33, and phosphor stripes 35 for indexing purpose are arranged in the horizontal direction so that the pitch of the phosphor stripes 35 is, for example, 2/3 of the interval of R, G, B sets of the phosphor stripes 31. When the phosphor stripes 31 are scanned by the single electron beam, the electron beam is incident on the phosphor stripes 35 to excite them, so that light is emitted from the phosphor stripes 35. The emitted light is detected by a light detector 36 to perform the feedback operation. This structure is disclosed in Japanese Patent Publication No. P61-61315.
Since prior art display units as mentioned above are of the beam-index type that uses an electron beam in an evacuated envelope (or a vacuum system), it has not proven possible to make the whole system lightweight. Moreover, adaptation of the picture size, especially change to a larger picture size, was not possible because of the fixed positional relation between the electron gun and the phosphor screen.